/Engine/Plugins/Runtime/RigVM/Source/RigVMDeveloper/Public/RigVMModel/Nodes/RigVMAggregateNode.h
The Aggregate Node contains a subgraph of nodes with aggregate pins (2in+1out or 1out+2in) connected to each other. For example, a unit node IntAdd which adds 2 integers and provides Result=A+B could have A, B and Result as aggregates in order to add additional input pins to construct an Aggregate Node that computes Result=A+B+C.
[UCLASS](Programming/UnrealArchitecture/Reference/Classes#classdeclaration)(BlueprintType) class URigVMAggregateNode : public [URigVMCollapseNode](API\Plugins\RigVMDeveloper\RigVMModel\Nodes\URigVMCollapseNode)